An electro-pneumatic compressed air control device of the type mentioned above is known from DE 44 21 575 A1. In a common housing an electro-pneumatic unloader as well as an electro-pneumatic multi-circuit control valve and an air-drier are provided. As control units for the unloader on the one hand and the different circuits of the multi-circuit control valve on the other hand, similar elements are provided in form of a check valve closing contrary to the flow direction. An actuation means consisting of a piston with a rod is associated to the check valve, the piston also being electrically controlled. The check valve of the unloader is an outlet valve in form of a safety valve opening to the atmosphere, whereas the check valve of the multi-circuit control valve opens to the different operation circuits. The check valve of the unloader can e.g. comprise an opening pressure of 13 bar which at the same time is the safety pressure of the compressed air control device. If for any reasons a higher pressure occurs in the chamber of the compressed air control device, the check valve of the unloader opens and limits the pressure in the chamber to the adjusted safety pressure. The check valves associated to the single circuits are also adjusted and in that way determine the corresponding circuit safety pressure. The adjustment of the check valves of the multi-circuit control valve with respect to the adjustment of the check valves of the unloader is problematic. When the check valves of the multi-circuit control valves are adjusted relatively high, e.g. to an opening pressure of 10 bar, in case of an interruption of the electronic a refillable container pressure of only 13 bar -10 bar=3 bar results. When the check valves of the circuits are adjusted relatively low, e.g. to an opening pressure of 3 bar, in case of an interruption of one of the circuits because of leakage, also the intact circuits can only be refilled with a pressure of 3 bar. Both defects, power interruption on the one hand and leakage in one circuit on the other hand, are realistic cases of damages and dangers. In the known compressed air control device an interruption of power on the one hand results in the described emergency features and on the other hand in the regeneration of the air-drier not taking place any more. When the vehicle is driven without power supply of the compressed air control device over a longer period of time this can lead to freezing of the non-regenerated air-drier in case of low temperatures and consequently to a total fail of the braking system.
In the German patent application 196 49 498.2 it has already been proposed to additionally integrate a mechanical-pneumatic unloader to the electro-pneumatic unloader, the mechanical-pneumatic unloader being adjusted to a switch-off pressure substantially higher than the switch-off pressure of the electro-pneumatic unloader. In that way the mechanical-pneumatic unloader is designed as on-off valve for turning on the regeneration phase of the air-drier after obtaining its switch-off pressure. The outlet valve in form of a safety valve is adjusted to a higher opening pressure than the switch-off pressure of the mechanical-pneumatic unloader. In this way additional to the electro-pneumatic unloader a mechanical-pneumatic unloader is integrated in the compressed air control device. While until now in the state of the art the development was to replace the mechanical-pneumatic unloader by an electro-pneumatic unloader, with respect to the defects described above, a mechanical-pneumatic unloader is chosen, the mechanical-pneumatic unloader being additionally provided to the electro-pneumatic unloader. In case of an intact device, which means correct power supply, the compressed air control device operates by means of the electro-pneumatic unloader. The mechanical-pneumatic unloader is not active, because its switch-off pressure is adjusted substantially higher than the switch-off pressure of the electro-pneumatic unloader. A substantially higher adjustment means an adjustment comprising a difference to the switch-off pressure of the electro-pneumatic unloader, so that e.g. in case of friction in the pneumatic part of the electro-pneumatic unloader, this cannot lead to an activation of the mechanical-pneumatic unloader. The mechanical-pneumatic unloader is only supposed to operate in case of a power interruption. It is clear that in case of correct power supply a correct regeneration of the air-drier in the known fashion takes place. But also in case of power interruption and controlling of the supply of the circuits by the mechanical-pneumatic unloader, a cyclic regeneration of the air-drier takes place. For this the mechanical-pneumatic unloader is also designed as an on-off valve for starting the regeneration phase of the air-drier. This regeneration phase takes place after achieving the switch-off pressure of the mechanical-pneumatic unloader. The outlet valve in form of a safety valve of the electro-pneumatic unloader is further adjusted to a higher opening pressure than the switch-off pressure of the mechanical-pneumatic unloader. This increased adjustment with respect to the state of the art is advantageous.
Thus, it is an object of this invention to provide an electro-pneumatic compressed air control device of the type described above, comprising an unloader, a multi-circuit control valve and an air-drier, the compressed air control device not only providing a filling of the circuits in case of power interruption but also enabling a regeneration of the air-drier in cases of intentional or unintentional power interruption.